The present invention relates to mounting structures for the rotor blades of a rotary wing aircraft and more particularly to a coupling system providing pitch adjustments of the blade and providing a redundant load path effective upon failure of the primary centrifugal load path.
It is conventional to attach the main rotor blades of a rotary wing aircraft to the mast by means of grip-yoke assemblies. These grip-yoke assemblies have elastomeric bearings for allowing relative rotational movement between the grip and yoke members while maintaining axial alignment between these members. Such assemblies utilize conventional tension strap and fittings or elastomeric thrust pads to transfer the centrifugal loads between the members. Since centrifugal blade loads are quite high, and since the main rotor blades provide essential lift forces for rotary wing aircraft, failure in the centrifugal load carrying system can create disastrous results.
The present invention is directed to an improved centrifugal load carrying system which provides a redundant centrifugal load path to allow continued operation of the aircraft if the primary centrifugal load carrying system fails.
More particularly, in the invention, a redundant centrifugal load structure is provided with a yoke structure connected to the hub of the rotor and a grip attached to the blade. The grip encloses the yoke and is held in radial alignment therewith by elastomeric radial bearings. A conventional tension strap or elastomeric thrust pad is attached between an inboard strap fitting on the inboard end of the yoke and an outboard strap fitting on the grip. A thrust bearing is mounted on the inboard end of the yoke and a transverse member with a corresponding bearing surface is provided on the grip inboard of the thrust bearing for engagement therewith upon failure of the primary thrust support system. In another embodiment, a bearing surface is formed on the outboard side of the outboard strap fitting and a thrust bearing is attached to the yoke outboard of the outboard strap fitting for contact upon failure of the primary centrifugal load carrying system.
The objectives and advantages of the present invention will be set forth in detail in the following description of the preferred embodiments of the invention with reference to the accompanying Drawings in which: